Q&A Powdery substance on brick

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QandA

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Nov 27, 2012
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Question:

We just noticed a yellowish, powdery substance on the brick on our fireplace in the living room.

It looks and feels like chalk and rubs off fairly easily.

It does not have a strong smell.

We have had a solid week of rain lately, so I'm wondering if it's some kind of mildew.

Any help out there?



Answer:

It sounds like a type of efflorescence, which comes from moisture as it seeps through the brick. This problem is often seen with chimneys venting gas appliances, but the root of an efflorescence problem is moisture. I recommend calling a professional chimney sweep to assess the cause and offer a cure. It may water entering through the mortar crown (the sloped area between the flue opening and the brick perimeter of the chimney), or you may have a problem with your flashing up on the roof. Removing the current stain won't help if you don't find the cause of the water leak.-Karen Duke Chimney Services
 
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